Chapter 49

[object Object],[object Object],[object Object],[object Object],OBJECTIVES: After studying Chapter 49, the reader should be able to:

[object Object],[object Object],KEY TERMS:

AIRFLOW MANAGEMENT ,[object Object],Continued ,[object Object],[object Object],[object Object],The use of these components allows the system to provide airflow under the following conditions: ,[object Object],[object Object],[object Object],[object Object]

Figure 49–1 The three major portions of the A/C and heat system are air inlet, plenum, and air distribution. The shaded portions show the paths of the four control doors. Continued

[object Object],[object Object],Continued ,[object Object],[object Object],[object Object],[object Object],[object Object]

[object Object],[object Object],Continued ,[object Object],[object Object],[object Object],[object Object]

[object Object],[object Object],[object Object],Afterblow is a term used to describe the operation of the blower motor after the ignition has been turned off. The purpose of afterblow is to dry the evaporator to help prevent the formation of mold and mildew in the evaporator case. The operation of the blower motor after the ignition is turned off has created some customer complaints. What is Afterblow? If the above conditions exist, the afterblow is commanded to be on for 20 seconds, off for 10 seconds, and back on for another 20 seconds. Check service information to be sure that the condition is normal or not on the vehicle being investigated. For example, in a typical General Motors system, the following conditions must be met for afterblow to occur:

Figure 49–2 The ambient temperature sensor in this system is located in the fresh air intake duct for the HVAC system. ,[object Object],Continued AUTOMATIC AIR-CONDITIONING Outside Air Temperature ( OAT ) Sensor Usually located at the front of the vehicle behind the grille but in front of the radiator. This sensor, commonly called the ambient air temperature sensor and is also supply temperature information for the driver on a display.

[object Object],NOTE: Some vehicles are equipped with a dual-zone sunload sensor that has two sensors included. This sensor allows the system to automatically adjust the airflow and air temperature based on the actual sun intensity experienced by both the driver and the passenger.

ACTUATORS ,[object Object],[object Object],Continued

Figure 49–3 A block diagram showing the inputs to the electronic control assembly and the outputs; note that some of the outputs have feedback to the ECM. See the chart on Page 567 of your textbook.

CABIN FILTERS ,[object Object],Continued

Figure 49–4 A typical cabin filter being removed from behind the glove compartment. NOTE: Some cabin filters contain activated charcoal which absorbs hydrocarbons and helps to deodorize the air as it enters the interior. For best results, use the designated replacement filter.

VACUUM CONTROL CIRCUITS ,[object Object],Figure 49–5 With no vacuum signal, the spring extends the actuator shaft to place the door in a certain position (top). A vacuum signal pulls the shaft inward and moves the door to the other position (bottom). Because vacuum decreases close to zero during heavy acceleration, a vacuum accumulator is used to store vacuum during short periods of acceleration.

ELECTRIC SERVOMOTOR CIRCUITS ,[object Object],Continued

Figure 49–6 Three electric actuators can be easily seen on this demonstration unit. However, accessing these actuators in a vehicle can be difficult. Figure 49–7 The feedback circuit signals the AC control unit with the blend door position.

BLOWER MOTOR CONTROL ,[object Object],Continued

Figure 49–8 A typical blower motor assembly with attached squirrel cage blower. A replacement motor does not include the squirrel cage blower so it needs to be switched to the replacement. Figure 49–9 A “credit card” resistor used in the rear blower assembly in a Dodge minivan.

DUAL-ZONE AIR CLIMATE CONTROL ,[object Object],Continued

Figure 49–10 A dual climate control system showing the airflow and how it splits.

REAR AIR-CONDITIONING SYSTEM ,[object Object],Continued Figure 49–11 A typical dual-zone climate control panel showing left and right side temperature control levers.

[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],Figure 49–12 Heated or cooled air is supplied to the rear seat passengers of most vehicles through ducts that run under the front seats. However, many larger vehicles require a separate heater core and air-conditioner evaporator in the rear to provide adequate heating and cooling. Most rear HVAC systems include the following components:

Figure 49–13 A sticker on a vehicle equipped with rear heat and air-conditioning warning that a special service procedure is needed when replacing engine coolant.

RECIRCULATION OPERATION ,[object Object],Continued

[object Object],HYBRID ELECTRIC VEHICLE HEATING AND COOLING SYSTEMS ,[object Object],[object Object],[object Object]

SUMMARY ,[object Object],[object Object],[object Object],Continued

SUMMARY ,[object Object],[object Object],[object Object],[object Object],( cont. )

Chapter 49

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Chapter 49